DVD technology comprises a wide and growing variety of disc and application specifications. Disc specifications include, for example, DVD-ROM for pre-recorded discs, DVD-R and DVD+R for write-once discs, and DVD-RW, DVD-RAM, and DVD+RW for rewritable discs. The disc format specifications generally define the physical characteristics of the disc (e.g., mechanical properties, optical signal characteristics, physical arrangement, writing methods, and testing conditions). Application specifications include DVD-Video for video content, DVD-Audio for audio content, and DVD-VR and DVD+VR for real-time video recording (e.g., in camcorders and personal video recorders [PVRs]).
The structure and format of data recorded to optical media is generally defined and described in the family of Universal Disk Format (UDF) specifications. The Optical Storage Technology Association (OSTA) has developed and implemented the UDF to enable file interchange among different operating systems and environments. In general, UDF was developed to implement the ISO/IEC 13346 specification (also known as ECMA 167). Whereas ISO/IEC 13346 is a broad, general standard for storing information on any media, the UDF specifically provides a standard for recording data to a plurality of recordable and rewritable optical media including CD-ROM, CD-Recordable (CD-R), and CD-Rewritable (CD-RW) as well as DVD-ROM, DVD-R, DVD-RW, DVD+R, DVD+RW, double density media, multi-layered media, and others. Although terms such as “operating system,” and the process of recording data, suggest a computer system environment, UDF is generally applicable to and defines the format for consumer CD audio devices for home and mobile audio systems, consumer DVD devices for both home and mobile DVD audio/visual systems, in addition to the many and varied computer system environments.
The UDF specification includes a number of revisions, some of which were developed and released to capture and implement standards for emerging and developing optical media technologies. By way of example, UDF Revision 1.02 includes standards and formats for DVD devices; UDF Revision 1.50 includes standards and formats for defect management and packet writing; UDF Revision 2.0 includes standards and formats intended to supersede Revision 1.50, and adds standards and formats for streaming and improved security control for optical media; and UDF Revision 2.01 includes standards and formats to update Revision 2.0, and adds standards and formats for real time files.
Multi-session and multi-border recording to optical media is an example of one advancement in optical media technology that was captured in the UDF specification during the periodic revision cycle. Prior to UDF Revision 1.50, no multi-session or multi-border standards or formats were implemented in the UDF. Beginning with UDF Revision 1.50, multi-session and multi-border recording is implemented in UDF. UDF Revision 1.02, however, does not include implementation of multi-session or multi-border recording, and therefore DVD devices compliant with UDF Revision 1.02 do not support multi-session or multi-border optical media. Consumer DVD devices such as, by way of example, DVD players used with television sets or audio/visual systems are generally UDF Revision 1.02 compliant, and therefore generally do not support or recognize multi-session or multi-border optical media. Generally, if a multi-session or multi-border DVD is inserted into a UDF Revision 1.02 compliant consumer DVD player, the consumer DVD player will only “see” one session. Typically, only the first session of the multi-session DVD is seen by the consumer DVD player, and therefore only the content of the first session is accessible for viewing.
The DVD-Video format was originally designed to meet the requirements of the film industry for distributing commercial movies on prerecorded (pressed) discs. Typically, discs written in DVD-Video format can be played back using most standards-compliant DVD video players or computer DVD-ROM drives employing appropriate software (subject to that device's physical compatibility with the specific type of disc). Recordable DVD formats may also contain DVD-Video data. Referring now to FIG. 1, DVD-Video data is shown on DVD-ROM, DVD+R, and DVD-R discs.
Due, in part, to the evolving nature of the DVD specifications, there can be mismatches between the application format and the capabilities of the disc format. For example, the DVD-Video format was initially designed to place static material on disc, and not to add to or change the material at a later time. To address this, several additional application formats were developed for use by consumer devices (e.g., writable DVD camcorders and consumer electronics [CE] recorders such as personal video recorders [PVRs]). Two of these new formats are the DVD-VR and DVD+VR real-time video formats. However, DVD-VR differs significantly from the original DVD-Video format. As a result, only devices specifically designed to be DVD-VR compatible (for example, units marked “RW compatible” and “DVD Multi”) can play DVD-VR recorded discs.
In many optical disc specifications, an optical disc may comprise two areas, including a user data area and a disc information (lead-in) area. The user data area is generally used to write application data, including video, audio, information tables, file system data, etc. The disc information (lead-in) area generally includes data such as disc size, disc type, disc layout, etc. In some optical disc specifications (e.g., DVD-R and DVD+R), any portion of the disc can be written only once, although subsequent titles may be recorded to previously unused portions of the disc.
In order to perform real-time recording (e.g., in camcorders and PVRs), data may generally be written to the user data area of the disc. Each time additional material is recorded to the disc, the additional data may be appended to the previously written data. Once the user wishes to playback the disc on a standard DVD-Video player, the user must generally “finalize” the disc, in order to populate the disc information (lead-in) area of the disc. Once the write-once disc is finalized, it is effectively a read-only disc, because the disc information (lead-in) area cannot be changed. Consequently, any remaining space on the disc is generally unusable. Therefore, it is desirable for read-only disc playing devices (e.g., consumer electronics DVD players) to read and play back data (e.g., DVD-Video) from unfinalized recordable discs.
A disc generally includes a sequence of error correction code (ECC) blocks. In the DVD standards, each ECC block generally contains 16 sectors of 2,048 data bytes each. Sectors are numbered with a 24-bit address. An ECC block generally further includes headers, error detection code (EDC) symbols, and ECC symbols. Individual sector data are generally interleaved in order to minimize the effects of large media flaws. These ECC blocks are generally recorded serially on the medium. In order to read and extract a single sector of data, a disc reader generally reads the ECC block containing the sector, applies error correction to the ECC block, and de-interleaves prior to extracting the data from the selected sector.
Typically, the finalized disc information (lead-in) area contains the location of the final ECC block on the disc. The final ECC block typically contains metadata such as volume structure information (e.g., Virtual Allocation Table [VAT] on DVD-R discs, or reserve space allocation table [RSAT] on a DVD+R disc). Therefore disc players generally must locate the final ECC block in order to retrieve volume information and read the data on the disc.
DVD-R and DVD+R discs can be either single or double-sided. A single-sided (SS) disc may include a recordable side and a non-recordable (“dummy”) side, while a double-sided (DS) disc may include two recording sides. The recording side of a DVD-R and DVD+R disc may include a number of layers. The substrate is generally a polycarbonate plastic containing a shallow spiral groove extending from the inside to the outside diameter of the disc. A DVD-R disc additionally includes “pits and lands” on the areas between the coils of the groove (land pre-pits). Added to this substrate is an organic dye recording layer (e.g., azo, cyanine, dipyrromethene or others), followed by a metal reflective layer (e.g., silver, silver alloy, gold). The non-recordable side of a single-sided disc generally includes an additional flat polycarbonate plastic substrate (sometimes with an additional metal layer to obscure the bonding layer from view for aesthetic purposes). An adhesive then bonds two recording sides (for a double-sided) or a recording and dummy side (for a single-sided) together into the final disc. Some single-sided discs are also topped on the dummy side with decorations or additional layers that provide surfaces suitable for labeling by inkjet, thermal transfer or re-transfer printers.
The first step in manufacturing a DVD-R or DVD+R disc is to fabricate the polycarbonate plastic substrates (incorporating the spiral groove and land pre-pits) using an injection molding process. The dye is then applied using spin coating and the metal layers by means of DC sputtering. After both sides of the disc are completed they are bonded together using a hot melt, UV cationic or free radical process. Additional decoration or printable layers are typically applied using screen printing methods. A DVD-R disc generally undergoes a further manufacturing step in which a specialized computer DVD recorder is used to “prewrite” information in the Control Data Zone of its Lead-in Area to inhibit direct copying of prerecorded DVD-Video discs encrypted with the Content Scrambling System (CSS).
DVD recording devices generally use a wobble signal transducer to demodulate the spiral groove and determine where data starts, the format of the discs, etc. Unlike DVD recording devices, many DVD players can not decode the wobble signal (e.g., address in pre-groove [ADIP] or pre-pit address encodings). Therefore, it may be difficult for such players to move the pick-up head(s) to the last metadata section of the disc and read the data back. Methods and devices for recording metadata sections to a disc such that disc playback devices can retrieve them from an unfinalized disc are described in U.S. patent application Ser. No. 11/403,375, filed Apr. 12, 2006, pending, the relevant portions of which are hereby incorporated by reference. Therefore, it is also desirable for disc playback devices to be able to access the data on these and other unfinalized discs.